Please tell me if i should use hardboiled eggs if i'm testing what kind of tooth paste auctually whitens?

I am not sure that: It would be a very valid experiment because the structure of an egg shell and a tooth vary greatly.

Save the eggs...: Save the eggs for breakfast. Any whitening toothpaste from one of the major manufacturers is about equally effective. Better whitening solution is custom trays and gels provided by your dentist. Tooth enamel and egg shells are structurally much different, so your experimental model is invalid.